In Rails 3.0, a Rails::Application object was introduced which is nothing more than an Engine but with the responsibility of coordinating the whole boot process.

Initialization

Rails::Application is responsible for executing all railties and engines initializers. It also executes some bootstrap initializers (check Rails::Application::Bootstrap) and finishing initializers, after all the others are executed (check Rails::Application::Finisher).

Configuration

Besides providing the same configuration as Rails::Engine and Rails::Railtie, the application object has several specific configurations, for example “cache_classes”, “consider_all_requests_local”, “filter_parameters”, “logger” and so forth.

Check Rails::Application::Configuration to see them all.

Routes

The application object is also responsible for holding the routes and reloading routes whenever the files change in development.

Middlewares

The Application is also responsible for building the middleware stack.

Booting process

The application is also responsible for setting up and executing the booting process. From the moment you require “config/application.rb” in your app, the booting process goes like this:

1)  require "config/boot.rb" to setup load paths
2)  require railties and engines
3)  Define Rails.application as "class MyApp::Application < Rails::Application"
4)  Run config.before_configuration callbacks
5)  Load config/environments/ENV.rb
6)  Run config.before_initialize callbacks
7)  Run Railtie#initializer defined by railties, engines and application.
    One by one, each engine sets up its load paths, routes and runs its config/initializers/* files.
8)  Custom Railtie#initializers added by railties, engines and applications are executed
9)  Build the middleware stack and run to_prepare callbacks
10) Run config.before_eager_load and eager_load! if eager_load is true
11) Run config.after_initialize callbacks
Namespace
Methods
A
C
E
I
K
L
N
R
S
Attributes
[RW] assets
[R] reloaders
[RW] sandbox
[RW] sandbox?
Class Public methods
inherited(base)

Source: show | on GitHub 

# File railties/lib/rails/application.rb, line 62
def inherited(base)
  raise "You cannot have more than one Rails::Application" if Rails.application
  super
  Rails.application = base.instance
  Rails.application.add_lib_to_load_path!
  ActiveSupport.run_load_hooks(:before_configuration, base.instance)
end
new()

Source: show | on GitHub 

# File railties/lib/rails/application.rb, line 77
def initialize
  super
  @initialized      = false
  @reloaders        = []
  @routes_reloader  = nil
  @app_env_config   = nil
  @ordered_railties = nil
  @railties         = nil
end
Instance Public methods
call(env)

Implements call according to the Rack API. It simply dispatches the request to the underlying middleware stack.

Source: show | on GitHub 

# File railties/lib/rails/application.rb, line 94
def call(env)
  env["ORIGINAL_FULLPATH"] = build_original_fullpath(env)
  env["ORIGINAL_SCRIPT_NAME"] = env["SCRIPT_NAME"]
  super(env)
end
env_config()

Stores some of the Rails initial environment parameters which will be used by middlewares and engines to configure themselves. Currently stores:

* "action_dispatch.parameter_filter"             => config.filter_parameters
* "action_dispatch.redirect_filter"              => config.filter_redirect
* "action_dispatch.secret_token"                 => config.secret_token
* "action_dispatch.secret_key_base"              => config.secret_key_base
* "action_dispatch.show_exceptions"              => config.action_dispatch.show_exceptions
* "action_dispatch.show_detailed_exceptions"     => config.consider_all_requests_local
* "action_dispatch.logger"                       => Rails.logger
* "action_dispatch.backtrace_cleaner"            => Rails.backtrace_cleaner
* "action_dispatch.key_generator"                => key_generator
* "action_dispatch.http_auth_salt"               => config.action_dispatch.http_auth_salt
* "action_dispatch.signed_cookie_salt"           => config.action_dispatch.signed_cookie_salt
* "action_dispatch.encrypted_cookie_salt"        => config.action_dispatch.encrypted_cookie_salt
* "action_dispatch.encrypted_signed_cookie_salt" => config.action_dispatch.encrypted_signed_cookie_salt

Source: show | on GitHub 

# File railties/lib/rails/application.rb, line 138
def env_config
  @app_env_config ||= begin
    if config.secret_key_base.blank?
      ActiveSupport::Deprecation.warn "You didn't set config.secret_key_base. " +
        "Read the upgrade documentation to learn more about this new config option."

      if config.secret_token.blank?
        raise "You must set config.secret_key_base in your app's config."
      end
    end

    super.merge({
      "action_dispatch.parameter_filter" => config.filter_parameters,
      "action_dispatch.redirect_filter" => config.filter_redirect,
      "action_dispatch.secret_token" => config.secret_token,
      "action_dispatch.secret_key_base" => config.secret_key_base,
      "action_dispatch.show_exceptions" => config.action_dispatch.show_exceptions,
      "action_dispatch.show_detailed_exceptions" => config.consider_all_requests_local,
      "action_dispatch.logger" => Rails.logger,
      "action_dispatch.backtrace_cleaner" => Rails.backtrace_cleaner,
      "action_dispatch.key_generator" => key_generator,
      "action_dispatch.http_auth_salt" => config.action_dispatch.http_auth_salt,
      "action_dispatch.signed_cookie_salt" => config.action_dispatch.signed_cookie_salt,
      "action_dispatch.encrypted_cookie_salt" => config.action_dispatch.encrypted_cookie_salt,
      "action_dispatch.encrypted_signed_cookie_salt" => config.action_dispatch.encrypted_signed_cookie_salt
    })
  end
end
initialized?()

Returns true if the application is initialized.

Source: show | on GitHub 

# File railties/lib/rails/application.rb, line 88
def initialized?
  @initialized
end
key_generator()

Return the application's KeyGenerator

Source: show | on GitHub 

# File railties/lib/rails/application.rb, line 107
def key_generator
  # number of iterations selected based on consultation with the google security
  # team. Details at https://github.com/rails/rails/pull/6952#issuecomment-7661220
  @caching_key_generator ||= begin
    if config.secret_key_base
      key_generator = ActiveSupport::KeyGenerator.new(config.secret_key_base, iterations: 1000)
      ActiveSupport::CachingKeyGenerator.new(key_generator)
    else
      ActiveSupport::LegacyKeyGenerator.new(config.secret_token)
    end
  end
end
reload_routes!()

Reload application routes regardless if they changed or not.

Source: show | on GitHub 

# File railties/lib/rails/application.rb, line 101
def reload_routes!
  routes_reloader.reload!
end
Instance Protected methods
allow_concurrency?()

Source: show | on GitHub 

# File railties/lib/rails/application.rb, line 370
def allow_concurrency?
  if config.allow_concurrency.nil?
    config.cache_classes
  else
    config.allow_concurrency
  end
end
load_rack_cache()

Source: show | on GitHub 

# File railties/lib/rails/application.rb, line 378
def load_rack_cache
  rack_cache = config.action_dispatch.rack_cache
  return unless rack_cache

  begin
    require 'rack/cache'
  rescue LoadError => error
    error.message << ' Be sure to add rack-cache to your Gemfile'
    raise
  end

  if rack_cache == true
    {
      metastore: "rails:/",
      entitystore: "rails:/",
      verbose: false
    }
  else
    rack_cache
  end
end
show_exceptions_app()

Source: show | on GitHub 

# File railties/lib/rails/application.rb, line 400
def show_exceptions_app
  config.exceptions_app || ActionDispatch::PublicExceptions.new(Rails.public_path)
end